UNIVERSITY  OF  CALIFORNIA  PUBLICATIONS 

IN 

AGRICULTURAL   SCIENCES 

Vol.  1,  No.  3,  pp.  39-49  December  14,  1912 


THE  EFFECTS  OF  CALCIUM  AND 
MAGNESIUM  CARBONATES  ON  SOME  BIO- 
LOGICAL TRANSFORMATIONS  OF 
NITROGEN  IN  SOILS 

BY 
W.  P.  KELLEY 


HISTORICAL  INTRODUCTION 

Loew1  and  his  co-workers  found,  some  years  ago,  that  the 
growth  of  a  number  of  plants  may  be  markedly  influenced  by 
variations  in  the  ratio  of  calcium  to  magnesium,  both  in  solution 
and  soil  cultures.  Osterhout2  also  showed  that  a  more  or  less 
definite  relation  between  other  elements  in  culture  solutions  is 
necessary  for  maximum  growth.  These  and  other  researches  have 
drawn  attention  to  certain  long  neglected  phases  of  plant  physi- 
ology and  strengthen  the  view  that  in  addition  to  the  mere 
presence  of  the  necessary  elements,  plants  also  demand  a  physio- 
logically balanced  relation  between  the  elements  in  solution  if 
maximum  growth  is  to  be  produced.  By  means  of  artificial  cul- 
ture solutions  principles  of  great  importance  are  being  worked 
out,  but  in  generalizing  from  culture  solutions  to  natural  soils, 
many  difficulties  arise.  The  great  complexity  of  the  factors  in- 
volved and  the  difficulties  inherent  in  the  question  necessitate 
the  greatest  care  in  making  broad  generalizations  regarding  soils. 


iLoew  and  May,  Bur.  Plant  Tnd.  U.  S.  D.  A.,  Bui.  No.  1;  Aso,  Bui. 
Col.  Agr.  Tokyo,  vol.  4,  pp.  361-370;  vol.  5,  p.  495;  vol.  6,  p.  97;  Loew  and 
Aso,  vol.  7,  pp.  395-407. 

2Bot.  Gaz.  42,  127-134;   44,  259-272;   48,  98-104. 


40  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

In  this  connection  the  "lime-magnesia  ratio"  has  become  a 
matter  of  general  interest  and  is  being  extensively  investigated 
at  the  present  time.  Some  recent  experiments  by  Lemmermann3 
and  others  seem  to  indicate  that  a  wide  variation  in  this  ratio  is 
of  no  consequence  to  plants.  It  is  well  known,  however,  that  the 
effects  produced  by  natural  limes  and  limestones  are  not  alwaj^s 
equal.  In  certain  instances  dolomitic  limes  are  known  to  produce 
less  favorable  results  than  non-magnesian  limes.  During  recent 
years  additional  light  on  the  action  of  lime  in  soils  has  been 
found  in  the  fact  that  calcium  carbonate  enhances  certain  bio- 
logical activities  through  supplying  an  active  base  by  means  of 
which  the  essential  neutral  condition  is  maintained.  In  this  con- 
nection the  question  of  the  effects  on  bacterial  activity  brought 
about  by  different  sources  of  lime  and  limestone  naturally  sug- 
gests itself. 

In  regard  to  physiologically  balanced  solutions  for  bacteria, 
Dr.  C.  B.  Lipman4  has  shown  that  the  ammonification  of  peptone 
by  pure  cultures  of  B.  sitbtilis  is  favored  on  the  one  hand  by  a 
certain  ratio  of  calcium  to  potassium,  magnesium  to  sodium  and 
potassium  to  sodium ;  while  on  the  other  hand,  he  failed  to  observe 
any  antagonism  between  calcium  and  magnesium  or  calcium  and 
sodium.  In  his  investigations  Lipman  found  that  a  certain  con- 
centration of  magnesium  chloride  proved  toxic  to  the  development 
and  activity  of  B.  subtilis  and  at  the  same  time  the  addition  of 
certain  amounts  of  calcium  chloride  failed  to  overcome  this  tox- 
icity. Likewise,  magnesium  or  sodium  was  ineffective  in  over- 
coming the  toxicity  of  calcium.  While  it  is  probably  true  that 
calcium  is  not  necessary  for  the  normal  development  of  bacteria, 
the  importance  of  these  observations,  if  found  to  apply  in  soils,  is 
at  once  obvious. 

From  a  study  of  the  effects  of  various  carbonates  on  the 
nitrification  of  ammonium  sulphate  in  solutions,  Owen5  in  1908 
concluded  that  magnesium  carbonate  is  better  suited  to  the  stimu- 
lation and  growth  of  nitrifying  organisms  than  calcium,  potas- 


3  Landw.  Jahrb.,  40  (1911),  pp.  173-254;  Also  see  Gile,  Porto  Rico  Sta. 
Ann.  Rept.,  1911. 

4Bot.  Gaz.,  48  (1908),  pp.  105-125;  49  (1909),  pp.  41-50. 
■•  Ota,.  Sta.  Bui.  81  (Technical  Series  No.  1),  1908. 


1912]  Kelley :  Biological  Transformations  of  Nitrogen  in  Soils  41 

sium  or  ammonium  carbonates.  It  is  but  fair  to  mention  in  this 
connection,  however,  that  great  dilution  of  these  carbonates  was 
employed. 

In  1910  Dr.  J.  G.  Lipman6  observed  that  the  addition  of  one 
gram  of  calcium  carbonate  per  one  hundred  grams  of  a  New  Jer- 
sey soil  stimulated  the  ammonification  of  dried  blood  but  de- 
pressed the  formation  of  ammonia  from  cotton  seed  meal.  In 
parallel  experiments  he  observed  that  an  equal  amount  of  mag- 
nesium carbonate  caused  a  depression  in  the  ammonification  of 
dried  blood  but  stimulated  the  ammonification  of  cotton  seed 
meal.  In  other  words,  the  ammonification  of  dried  blood  and  cot- 
ton seed  meal  in  one  and  the  same  soil  were  affected  by  calcium 
and  magnesium  carbonates  in  opposite  ways,  both  as  regards  the 
carbonates  and  the  nitrogenous  substances  employed.  These  re- 
sults are  interesting  and  suggestive  and  point  to  the  complexity 
of  this  single  step  in  the  preparation  of  available  nitrogen  from 
the  organic  substances  occurring  in  soils. 

In  the  same  year  Kellerman  and  Robinson7  pointed  out  that 
the  addition  of  magnesium  carbonate  to  a  highly  magnesian  soil 
in  quantities  above  0.25  per  cent  greatly  depressed  the  formation 
of  nitrates  while  the  application  of  calcium  carbonate  in  quanti- 
ties up  to  2  per  cent  markedly  stimulated  nitrification.  The 
growth  of  crops  on  this  soil  had  been  found  to  be  much  more 
favorably  influenced  by  the  application  of  ground  oyster  shells 
than  by  magnesium  limestone.  The  authors  inferred  from  their 
experiments  that  the  inferior  effects  on  crops  following  the  appli- 
cation of  dolomitic  limestone  may  be  due,  in  part,  to  retarded 
nitrification. 

AMMONIFICATION 

In  the  course  of  some  studies  on  soil  bacteriology  at  the  Uni- 
versity of  California,  the  writer  undertook  a  study  of  certain 
biological  transformations,  as  affected  in  two  different  sandy  soils 
from  California  by  varying  amounts  and  combinations  of  calcium 
and  magnesium  carbonates.  On  account  of  the  striking  nature 
of  the  results  obtained  in  the  preliminary  ammonification   ex- 


e  N.  J.  Sta.  Kept.,  1910. 
7  Science,  32,  p.  159. 


42  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

periments  a  systematic  study  of  this  question  was  undertaken. 
The  soil  employed  in  the  ammonification  experiments  presently 
to  be  described  was  of  a  light  sandy  character  having  been  taken 
from  near  Oakley  in  the  upper  part  of  San  Joaquin  Valley  and 
represents  a  large  area  now  devoted  to  the  growth  of  peaches 
and  other  fruits.  With  suitable  moisture  conditions  this  land 
produces  excellent  growth  of  the  crops  suited  to  it.  The  followT- 
ing  analysis  furnished  by  the  courtesy  of  Dr.  Lipman  sets  forth 
the  composition  of  this  soil. 

Table  I.     Composition  of  Soil  Used  in   Ammonification  Experiments 

Per  cent 
Insoluble  matter  80.45 

Soluble  silica   6.15 

Potash  (K20)   0.35 

Soda  (Na20)  0.15 

Lime  (Ca  O)  1.41 

Magnesia   (Mg  O)    0.33 

Br.  Ox.  Manganese  (Mn:.04)  0.09 

Ferric  Oxide   (Fe2Oy)   3.96 

Alumina    (AL03)    4.45 

Phosphoric  Acid  (P20.)   0.10 

Sulphuric  Acid   (S  0:;)   0.06 

H20  at  110°  C 0.80 

Volatile  matter   2.02 

Total    100.32 

In  the  ammonification  experiments  dried  blood  was  used  as  a 
source  of  nitrogen.  Five  grams  of  this  material  and  varying 
amounts  of  calcium  and  magnesium  carbonates  were  thoroughly 
mixed  with  100  gram  portions  of  sifted  soil,  placed  in  tumblers 
and  then  optimum  moisture  conditions  provided  by  the  addition 
of  sterile  water.  The  tumblers  were  covered  with  Petri  dishes 
and  after  an  incubation  period  of  seven  days  the  ammonia  was 
distilled  into  standard  acid  by  the  use  of  magnesium  oxide  and 
measured  in  the  usual  way.  The  results  are  recorded  in  the 
following  table. 


1912]  Kelley:  Biological  Transformations  of  Nitrogen  in  Soils  43 

Table  II.    Effects  of  Calcium  and  Magnesium  Carbonates  on  the 
Ammonification  of  Dried  Blood 

Ammonia  nitrogen 
Treatment  mgs. 

None     81.4 

1  Gram  Calcium  Carbonate  84.3 

2  Gram  Calcium  Carbonate  85.0 

4     Gram  Calcium  Carbonate  91.0 

6     Gram  Calcium  Carbonate  91.0 

8     Gram  Calcium  Carbonate  87.8 

12  Gram  Calcium  Carbonate  87.8 

1  Gram  Magnesium  Carbonate  53.2 

2  Gram  Magnesium  Carbonate  53.9 

4     Gram  Magnesium  Carbonate  50.0 

These  data,  as  all  others  submitted  in  this  paper,  represent 
averages  of  closely  agreeing  duplicates.  In  examining  the  above 
data  we  note  a  slight  stimulation  in  ammonia  formation  from  the 
use  of  the  several  amounts  of  calcium  carbonate  employed,  the 
maximum  stimulation  being  reached  with  from  4  to  6  grams  per 
100  grams  of  soil.  With  the  use  of  magnesium  carbonate  a  marked 
depression  in  ammonia  accumulation  occurred,  there  having  been 
found  to  be  a  falling  off  of  approximately  one-third  as  compared 
with  the  amounts  found  without  the  use  of  carbonate.  It  is  also 
noteworthy  that  one  gram  of  magnesium  carbonate  proved  to  be 
about  as  toxic  to  ammonification  as  larger  amounts. 

A  second  series  was  prepared  with  the  use  of  still  smaller 
amounts  of  magnesium  carbonate  for  the  purpose  of  determining 
the  concentration  at  which  toxic  effects  begin  and  also  to  deter- 
mine the  minimum  amount  of  this  carbonate  necessary  to  produce 
maximum  toxicity.    The  results  follow. 

Table  III.     Ammonification  of  Dried  Blood  as  Affected  by  Small 
Amounts  of  Magnesium  Carbonate 

Ammonia  nitrogen 
Treatment  mgs. 

None     93.1 

0.1  Gram  Magnesium  Carbonate  77.4 

0.2  Gram  Magnesium  Carbonate  70.6 

0.4  Gram  Magnesium  Carbonate  65.6 

0.6  Gram  Magnesium  Carbonate  65.2 

0.8  Gram  Magnesium  Carbonate  64.6 

1.0  Gram  Magnesium  Carbonate  62.0 


44  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

These  data  are  instructive  as  showing  the  marked  depression 
of  ammonification  in  the  soil  employed,  even  with  the  small 
amount  of  .1  per  cent  of  magnesium  carbonate.  The  toxicity  in- 
creased with  greater  amounts  of  the  magnesium  carbonate  added 
reaching  a  practical  maximum  with  from  0.8  to  1  gram  per  100 
grams  of  soil. 

According  to  Loew  the  toxic  effects  of  an  excess  of  magnesia 
in  soils  can  be  overcome  or  antagonized  by  the  application  of 
lime.  While  this  theory  was  proposed  and  held  for  the  higher 
plants,  it  was  thought  to  be  of  some  interest  to  study  the  question 
with  reference  to  the  ammonification  process.  Accordingly  the 
following  series  of  experiments  was  arranged.  In  these  trials  one 
gram  of  magnesium  carbonate  per  100  grams  of  soil  was  used 
throughout,  this  quantity  having  been  found  to  be  the  lowest 
that  produced  maximum  toxicity. 

Table  IV.     Ammonification  of  Dried  Blood  in  the  Presence  of  Both 

CaCo    and  MgCo 

3  3 

Ammonia  nitrogen 
Treatment  mgs. 

1  Gram  Calcium  Carbonate  84.3 

1  Gram  Magnesium  Carbonate  53.9 

1  Gram  Magnesium  Carbonate  4-  0.5  Grams  Calcium  Carbonate  51.1 
1  Gram  Magnesium  Carbonate  4-  1.  Grams  Calcium  Carbonate  53.9 
1  Gram  Magnesium  Carbonate  4-  2.  Grams  Calcium  Carbonate  53.2 
1  Gram  Magnesium  Carbonate  4-  3.  Grams  Calcium  Carbonate  50.6 
1  Gram  Magnesium  Carbonate  4-  4.  Grams  Calcium  Carbonate  51.1 
1  Gram  Magnesium  Carbonate  4-  5.  Grams  Calcium  Carbonate  50.7 
1  Gram  Magnesium  Carbonate  4-  6.  Grams  Calcium  Carbonate  50.3 
1  Gram  Magnesium  Carbonate  4-  8.  Grams  Calcium  Carbonate  50.7 
1  Gram  Magnesium  Carbonate  4-12.  Grams  Calcium  Carbonate  50.4 

From  these  data  it  is  at  once  seen  that  no  antagonism  was 
produced.  Even  the  very  large  amount  of  12  grams  of  calcium 
carbonate  in  no  way  reduced  the  toxic  effects  produced  by  one 
gram  of  magnesium  carbonate.  The  results,  therefore,  are  in 
harmony  with  the  observations  made  by  Dr.  C.  B.  Lipman8  in  his 
studies  on  the  physiology  of  B.  subtilis. 


*  Loc.  cit. 


1912]  Kelley :  Biological  Transformations  of  Nitrogen  in  Soils  45 


NITRIFICATION 

Having  failed  to  observe  any  antagonism  between  calcium  and 
magnesium  in  the  complex  process  of  ammonification  in  the  soil 
under  investigation,  attention  was  directed  to  a  study  of  nitrifica- 
tion under  similar  conditions.  A  sandy  soil  from  Anaheim,  Cali- 
fornia, that  contained  a  vigorous  nitrifying  flora,  was  employed 
in  these  studies.  The  following  table  of  analyses  furnished  by 
the  kindness  of  Dr.  Lipman  shows  the  chemical  composition  of 
this  soil. 

Table  V.    Composition  of  Soil  Used  in  Nitrification  Experiments 

Per  cent 

Insoluble  matter   73.59 

Soluble  Silica  11.17 

Potash  (K,0)   64 

Soda  (Na20)  15 

Lime  (Ca  O)  1.39 

Magnesia   (Mg  O)    93 

Br.  Ox.  Manganese  (Mn304)  04 

Ferric  Oxide   (Fe203)   5.10 

Alumina    (Al263)    3.92 

Phosphoric  Acid  (PA,)  12 

Sulphuric  Acid   (SO,)   02 

Volatile  matter 


I 


H20  at  110°  C 


Total    99.95 

The  nitrification  experiments  were  carried  out  in  tumblers, 
two  grams  of  dried  blood  being  mixed  with  each  100  gram  portion 
of  soil.  The  amounts  of  calcium  and  magnesium  carbonates  added 
are  shown  in  the  table.  Optimum  moisture  conditions  were  main- 
tained throughout  the  21  day  incubation  period  during  which 
time  a  temperature  of  27  to  28  degrees  was  maintained.  The 
results  are  shown  in  the  following  table. 


46  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


Table  VI.    Effects  of  Calcium  and  Magnesium  Carbonates  on  the 
Nitrification  of  Dried  Blood 

Nitrate  nitrogen 
Treatment  found  mgs. 

None     14.5 

1.0  Gram  Calcium  Carbonate  23.5 

2.0  Gram  Calcium  Carbonate  19.2 

4.0  Gram  Calcium  Carbonate  21.2 

8.0  Gram  Calcium  Carbonate  20.2 

0.1  Gram  Magnesium  Carbonate  3.6 

0.2  Gram  Magnesium  Carbonate  2.9 

0.4  Gram  Magnesium  Carbonate  2.8 

0.8  Gram  Magnesium  Carbonate  5.1 

1.0  Gram  Magnesium  Carbonate  1.0 

2.0  Gram  Magnesium  Carbonate  2.0 

4.0  Gram  Magnesium  Carbonate  2.9 

8.0  Gram  Magnesium  Carbonate  3.3 

Original  soil  5.0 


It  will  be  observed  that  while  approximately  a  50  per  cent 
stimulation  in  nitrate  formation  was  effected  by  the  addition  of 
calcium  carbonate,  nitrification  was  totally  inhibited  by  the  addi- 
tion of  one-tenth  of  one  gram  of  magnesium  carbonate.  Before 
further  discussing  these  results  the  data  obtained  from  the 
effects  of  calcium  and  magnesium  carbonates  acting  synchron- 
ously will  be  presented. 


Table  VII.    The  Lack  of  Antagonism  Between  Calcium  and  Magnesium 
Carbonates  as  Shown  in  the  Nitrification  of  Dried  Blood 

Nitrate  nitrogen 
Treatment  found  mgs. 

None       14.5 

1.0  gram  Calcium  Carbonate  23.5 

0.1  gram  Magnesium  Carbonate  3.6 

0.1  gram  Magnesium  Carbonate  and  1.  gram  Calcium  Carbonate  4.1 

0.1  gram  Magnesium  Carbonate  and  2.  gram  Calcium  Carbonate  3.4 

0.1  gram  Magnesium  Carbonate  and  3.  gram  Calcium  Carbonate  2.6 

0.2  gram  Magnesium  Carbonate  and  1.  gram  Calcium  Carbonate  1.9 

0.2  gram  Magnesium  Carbonate  and  2.  gram  Calcium  Carbonate  1.4 

0.2  gram  Magnesium  Carbonate  and  3.  gram  Calcium  Carbonate  2.0 

0.4  gram  Magnesium  Carbonate  and  1.  gram  Calcium  Carbonate  2.2 

0.4  gram  Magnesium  Carbonate  and  2.  gram  Calcium  Carbonate  1.8 

0.4  gram  Magnesium  Carbonate  and  3.  gram  Calcium  Carbonate  3.1 

0.8  gram  Magnesium  Carbonate  and  1.  gram  Calcium  Carbonate  2.9 

0.8  gram  Magnesium  Carbonate  and  2.  gram  Calcium  Carbonate  3.5 

0.8  gram  Magnesium  Carbonate  and  3.  gram  Calcium  Carbonate  4.1 


1912]  Kelley :  Biological  Transformations  of  Nitrogen  in  Soils  47 

Here  again  it  is  shown  that  .1  gram  of  magnesium  carbonate 
per  100  grams  of  soil  entirely  prevented  nitrification.  Neither 
do  we  observe  any  effective  antagonism  through  the  use  of  cal- 
cium carbonate. 

On  the  one  hand  it  was  found  that  ammonification  of  dried 
blood  was  seriously  interfered  with  by  the  presence  of  small 
amounts  of  magnesium  carbonate,  and  on  the  other,  nitrification 
was  completely  prevented  by  its  presence.  In  neither  case  was 
there  any  evidence  of  an  antagonism  between  magnesium  and 
calcium  carbonates.  In  the  above  nitrification  experiments,  mag- 
nesium carbonate  not  only  prevented  the  formation  of  nitrates 
but  at  the  same  time  induced  a  reduction  in  the  amounts  of 
nitrates  originally  present  in  the  soil.  It  was  observed  that  with 
the  addition  of  magnesium  carbonate  a  much  more  abundant 
growth  of  moulds  took  place  than  in  the  tumblers  receiving  cal- 
cium carbonate. 

With  a  view  of  throwing  further  light  on  this  question,  total 
nitrogen  was  determined,  both  before  and  after  the  incubation 
period  of  21  days,  in  a  similar  set  of  experiments  to  which  one 
gram  of  magnesium  carbonate  had  been  added.  The  result  showed 
that  during  the  period  of  bacterial  action,  similar  to  that  in  the 
preceeding  nitrification  experiments,  the  soil  sustained  a  loss 
equal  to  about  20  per  cent  of  the  combined  nitrogen  originally 
present. 

Two  factors  suggest  themselves  as  bearing  on  this  question. 
The  first  and  probably  most  important  is  that  of  volatilization 
and,  therefore,  loss  of  ammonia.  J.  G.  Lipman9  in  his  numerous 
researches  found  that  the  dilution  of  a  heavy  silt  loam  with 
silica  sand  caused  a  loss  of  ammonia  in  ammonification  experi- 
ments. The  loss  began  to  manifest  itself  with  the  use  of  30  per 
cent  of  sand  but  greatly  increased  with  larger  amounts.  This 
loss  was  attributed  to  the  volatilization  of  ammonia  and  was 
sufficiently  great  to  give  an  appreciable  odor  of  ammonia  above 
the  tumblers.  The  soils  employed  in  the  experiments  herein 
described  were  largely  composed  of  sand  and  contained  very 
small  amounts  of  silt  and  clay.  The  substances  capable  of  fixing 
large  amounts  of  ammonia  are,  therefore,   largely  absent  from 


N.  J.  Sta.  Kept.,  1909. 


48  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

these  soils  and  consequently  considerable  loss  may  have  been 
sustained  through  the  volatilization  of  ammonia.  The  data  on 
ammonification,  therefore,  should  be  considered  as  representing 
the  ammonia  accumulated  rather  than  the  absolute  amounts 
formed.  The  relative  effects  of  calcium  and  magnesium  carbon- 
ates on  the  loss  of  ammonia  were  not  investigated. 

A  second  factor  in  the  loss  of  nitrogen  is  that  of  denitrifica- 
tion.  It  was  recently  shown  by  Vogel10  that  calcium  carbonate 
under  certain  conditions  can  bring  about  a  considerable  loss  of 
nitrogen  as  nitrates  in  soils  through  denitrification.  In  the  pre- 
vious experiments  it  was  observed  that  with  the  use  of  magnesium 
carbonate  a  decided  reaction  for  nitrites  could  be  obtained.  Deni- 
trification, therefore,  took  place  and  an  actual  loss  of  nitrogen 
is  probably  traceable  to  this  cause.  From  the  preceding  data 
(Table  VI)  it  is  seen  that  the  use  of  small  amounts  of  magnesium 
carbonate  not  only  inhibited  nitrification  but,  as  previously  men- 
tioned, also  caused  a  considerable  loss  of  the  nitrates  already  in 
the  soil.  We  have  here,  therefore,  still  further  evidence  of  deni- 
trification having  taken  place.  "With  the  use  of  larger  amounts 
of  magnesium  carbonate,  nitrification  and  denitrification  were 
both  inhibited  but  no  considerable  loss  of  the  nitrates  originally 
present  in  the  soil  took  place. 

It  seems  probable,  therefore,  that  the  smaller  amounts  of  mag- 
nesium carbonate  were  toxic  to  the  nitrifying  bacteria  while  still 
allowing  the  denitrifiers  to  act,  but  under  the  influence  of  larger 
amounts  of  magnesium  carbonate  both  the  nitrifying  and  deni- 
trifying groups  were  rendered  inactive. 

The  striking  nature  of  the  results  obtained  in  the  previous 
ammonification  and  nitrification  experiments  suggested  a  study 
of  nitrogen  fixation  under  similar  conditions.  For  this  purpose 
the  Anaheim  soil  was  employed  since  it  contains  a  vigorous  nitro- 
gen fixing  flora.  Mannite  was  used  in  these  experiments  and 
the  usual  method  followed.  The  results  obtained  proved  to  be  so 
irregular  and  discordant  that  their  publication  is  withheld  at  this 
time.  In  one  series  a  slight  decrease  in  the  amount  of  nitrogen 
fixed  followed  the  use  of  magnesium  carbonate,  while  in  still 
another  series  no  effects  were  observed. 


"><VhlU.  lisikt.  ,'J4,  pp.  540-561. 


1912]  Kelley:  Biological  Transformations  of  Nitrogen  in  Soils  40 


DISCUSSION 

The  experimental  data  presented  above  show  that  under  the 
conditions  employed  and  in  the  soils  studied,  calcium  carbonate 
stimulated  the  ammonification  of  dried  blood  to  a  limited  extent 
but  exercised  a  more  noteworthy  stimulating  effect  on  nitrifica- 
tion. With  magnesium  carbonate  a  pronounced  toxic  effect  was 
produced.  In  the  ammonification  of  dried  blood  there  was  sus- 
tained a  loss  of  about  one-third  as  compared  with  the  experiments 
without  the  use  of  carbonates,  while  in  the  nitrification  experi- 
ments magnesium  carbonate  completely  inhibited  nitrate  forma- 
tion. It  is  also  noteworthy  that  no  evidence  of  antagonism  be- 
tween calcium  and  magnesium  carbonates  was  observed.  It  is 
not  intended,  however,  to  generalize  from  these  results.  It  does 
not  follow  that  similar  results  would  be  obtained  from  any  soil. 
In  fact,  data  already  obtained  from  other  soils  show  that  the 
phenomena  observed  in  the  two  soils  above  discussed  are  not  of 
universal  occurrence  under  similar  conditions. 

A  further  study  of  the  lime-magnesia  ratio  in  reference  to 
nitrogen  transformations  in  soils  is  now  under  way  with  the 
use  of  several  types  of  Hawaiian  soils  and  interesting  results  have 
already  been  obtained.  A  more  complete  interpretation  of  the 
results  obtained  is  reserved  for  a  subsequent  publication  after  a 
wider  range  of  observations  have  been  made.  Before  a  satis- 
factory understanding  of  the  lime-magnesia  question  in  regard 
to  field  crops  is  presented  it  is  imperative  that  we  have  more 
specific  knowledge  concerning  the  effects  produced  on  the  various 
organisms  of  soils,  now  generally  admitted  to  be  of  fundamental 
importance  in  plant  growth,  and  it  is  especially  important  that 
the  effects  produced  on  the  organisms  affecting  nitrogen  trans- 
formations be  more  fully  understood.  It  is  hoped  that  this  work 
may  stimulate  other  investigations  along  this  line. 

The  author  wishes  to  extend  his  thanks  to  Dr.  C.  B.  Lipman, 
in  whose  laboratory  this  work  was  carried  out,  for  many  valuable 
suggestions  offered  from  time  to  time  and  the  great  interest 
shown. 


